Mars rover Spirit has made its last short drives of the season and is now parked for the Martian winter. Spirit, which has been roaming the red planet landscape for six years, has entered a state of suspended operation called "safe mode" due to low power.

NASA is worried that Spirit will not survive the winter. Spirit has spent the past three winters with a maximum tilt for sunshine. But this year, Space.com reports that Spirit hasn't been able to maximize its tilt to catch as much of the low winter sun's rays as possible. In fact, it is going to be tilted 9 degrees to the south, as opposed to its usual northern tilt. 

Steven Squyres is the rover mission's principal investigator at Cornell University in Ithaca, N.Y. As Squyers told Space.com, "We have hope that Spirit will survive this cold, dark winter that we have ahead of us and be ready to do more science come springtime."

In hopes to preserve the rover, NASA is sending it into a state of winter hibernation. It is expected to power down with just enough energy to keep its master clock running and check its power status periodically until it has enough power to turn back on. Experts are hopeful that the rover will actually obtain enough power over the winter to come “back to life.”

Further, scientist have programmed the rover to take a series of "before" images of its surroundings. Scientists hope to compare the images with what it looks like in the Martian spring to see how the winter winds carved out the landscape. A robot arm is also being positioned to study atmospheric conditions.

And just how cold does it get during a Martian winter? During the time of polar darkness, it gets so chilly that CO2, the primary constituent of the Martian atmosphere, turns from a gas to a solid. Experts point out that so much carbon dioxide freezes out of the atmosphere that the global atmospheric pressure decreases by 25 percent.

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